(1) Field of the Invention
This invention relates to a method and an apparatus for developing photoresist film patterns on substrates such as semiconductor wafers, glass substrates for liquid crystal displays, glass substrates for photomasks, and substrates for optical disks. More particularly, the invention relates to a technique of developing film patterns (in what is called puddle development) with a developer spread and retained on substrates utilizing the surface tension thereof.
(2) Description of the Related Art
FIG. 1 shows an apparatus of the type noted above. A conventional developing technique will be described with reference to this figure.
In FIG. 1, reference W denotes a substrate such as a semiconductor wafer, an upper surface thereof being formed with a photoresist film having a predetermined thickness and a predetermined pattern printed and exposed thereon. The wafer W is suction-supported in a substantially horizontal position on a spin chuck 1. The spin chuck 1 is surrounded by a scatter preventive cup 4 for collecting a developer and the like. The scatter preventive cup 4 includes, disposed in lower positions thereof, drain ports 8 for draining used developer and the like, and exhaust ports 10 for exhausting a gas including mist of the developer scattering within the cup 4. A cylindrical wall 13 is continuous with an upper end of the scatter preventive cup 4 for preventing the odor of the developer and the like from diffusing to the ambient. The apparatus further includes a nozzle 16 for supplying the developer to the vicinity of the spin center of wafer W.
With the apparatus having the above construction, when the wafer W is suction-supported on the spin chuck 1, developer L is delivered from the nozzle 16 to make puddle the wafer W. A developing process takes place in this state. Upon completion of development, the spin chuck 1 is driven to spin at a high speed to spread the developer from the wafer W. At the same time, a different nozzle, not shown, is moved to a position above the wafer W to jet out a cleaning liquid, such as deionized water, for cleaning the wafer W. The wafer W is maintained in the spinning state for a fixed time after stopping the cleaning liquid. As a result, the wafer W is stripped of the cleaning liquid supplied thereto, and is allowed to dry.
During this developing process, down-ward flows of clean air DF in the cleanroom in which the developing apparatus is installed are taken into the scatter preventive cup 4 through an upper opening of the cylindrical wall 13, and forcibly exhausted through the exhaust ports 10 in the lower positions of the scatter preventive cup 4. These downflows DF prevent the odor of the developer from diffusing outside the apparatus, and mist of the developer and the like generated in the scatter preventive cup 4 from adhering to the upper surface of wafer W.
The conventional apparatus having the above construction has the following disadvantages.
During the developing process with the developer spread over the wafer W, the conventional apparatus takes downflows DF into the scatter preventive cup 4 and exhausts the downflows through the lower positions thereof. Consequently, gas flows downward around the edge of wafer W during the developing process, whereby the developer vaporizes at a higher rate from adjacent the edge of the wafer than from a central region of the wafer. The part of the developer adjacent the wafer's edge gives up a high heat of vaporization. As a result, peripheral regions of the wafer become cooler than the central region thereof, with a sharp temperature gradient from center to edge (i.e. lowering toward the edge). Thus, the conventional apparatus has the disadvantage of producing uneven developing (i.e. non-uniformity in the line width of a pattern developed). Specifically, where the temperature of the developer is around 23.degree. C., the developer temperature and an average line width of the developed pattern are in a relationship of approximately 0.01 .mu.m/.degree.C. The lower the temperature, the thinner the line width of the pattern tends to be (with the higher rate of development). Thus, this uneven developing results mainly in the line width of the pattern becoming gradually thinner from the center to the edge of wafer W.
To avoid such uneveness in developing, the temperature gradient may be eliminated by stopping the gas exhaust from the scatter preventive cup 4 during the developing process. However, this measure will bring about the following inconvenience.
The region of wafer W directly under the nozzle 16, e.g. the central region of wafer W, constantly receives a fresh supply of the developer from nozzle 16. Consequently, the part of the photoresist film in the central region is in constant contact with the developer having high activity. On the other hand, the peripheral regions of wafer W receive the developer spread from the central region. The developer reacts with the photoresist film while spreading from the central region to the peripheral regions, and its effectiveness has been reduced by the time the developer reaches the peripheral regions and acts on the photoresist film. That is, the effectiveness of the developer lowers gradually from the central region to the peripheral regions of the wafer. As a result, the developed pattern has a thinner line width in the central region than in the peripheral regions. In other words, an uneveness in developing occurs from a different cause that development progresses at a higher rate in the central region than in the peripheral regions.